STRUCTURE DETERMINATION OF A NEW TERNARY TH-NI-AL PHASE USING ELECTRON DIFFRACTION TOMOGRAPHY METHOD

Th-Ni-Al system was studied numerously both as part of a larger A-T-Al system (where A are actinides and T-transition metals) due to the possible heavy fermion formation and as capable of reversible absorption of hydrogen [1, 2, for example]. In the framework of the study of the Th-Ni-Al system, our group revealed three new ternary aluminides. Although alloy of an interest was exposed to prolonged heat treatment, it did not attained an equilibrium state. Eventually, all three unknown ternary phases remained in the alloy. Thus, structural study using traditional X-ray diffraction methods was impossible.

Current research was undertaken with a purpose to solve the structure of the major Th₂Ni₁₀Al₁₅ phase using Electron Diffraction Tomography (EDT) method [3,4]. Since the atomic structure of aluminides belonging to the A-T-Al systems was never solved using this approach, first, known ThV₂Al₂₀ phase was used as a case-study. Then, the atomic structure of the new Th₂Ni₁₀Al₁₅ phase was solved using direct methods applied to the EDT data. It should be noted that the success of the solution of such structure from EDT data is not obvious since the Fourier difference map is obscured by the actinide atoms, making it almost impossible to refine the positions of Al.

[1] H. R. Ott, Annu. Rev. Mater. Sci., 17 (1987) 13.

[2] T. Takeshita and W. E. Wallace, J. Less-Common Met., 55 (1977) 61.

[3] U. Kolb, T. Gorelik, C. Kübel, M. T. Otten, and D. Hubert, Ultramicroscopy, 107 (2007) 507.

[4] M. Gemmi and P. Oleynikov, Zeitschrift für Krist. - Cryst. Mater., 228 (2013) 51.